The present application relates to an organic EL light-emitting material and an organic EL light-emitting element, which uses the organic EL light-emitting material, for display devices such as flat light sources and color displays.
In recent years, display devices using an organic electroluminescent element (so-called organic EL light-emitting element) have been attracting attention as a flat panel display with small power consumption, high response speed and no viewing angle dependence.
In general, organic EL light-emitting elements have an organic layer inserted between a cathode and an anode, in which holes and electrons injected from the anode and cathode, respectively, recombine in the organic layer to emit light. As the organic layer, there are developed, for example, such constructions as a stack of a hole transport layer, a light-emitting layer including a light-emitting material, and an electron transport layer in this order from the anode side and a stack of those layers in which an electron transport layer further includes a light-emitting material to work as a light-emitting layer having an electron transport property.
Regarding a light-emitting material, after the announcement of EL emission by means of a phosphorescent compound (iridium complex) by a group of Baldo et. al. in 2000 (See Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Nature 2000, 403, 750-753.), improvements of tris- and bis-cyclometalated iridium (III) complex by chemical modification have energetically been performed (See Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H. E.; Adachi, C.; Burrows, P.; Forrest, S. R.; Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4304-4312.).
For example, it has come to realize that in fluorinated derivatives, a triplet-triplet quenching process is suppressed and further, sublimation properties of the complex are improved (See Grushin, V. V.; Herron, N.; LeCloux, D. D.; Marshall, W. J.; Petrov, V. A.; Wang, Y. Chem. Commun. 2001, 1494-1495.), and that self-quenching can be suppressed by introducing a group having a large steric hindrance (See Xie, H. Z.; Liu, M. W.; Wang, O. Y.; Zhang, X. H.; Lee, C. S.; Hung, L. S.; Lee, S. T.; Teng, P. F.; Kwong, H. L.; Hui, Z.; Che, C. M. AdV. Mater. 2001, 13, 1245-1248.). In addition, regarding lanthanide-based phosphorescent materials, there are some of materials that are presented in review paper by Kido et. al. (See Kido. J.; Okamoto, Y. Chem. Rev. 2002, 102, 2357-2368.).
However, these complexes use a rare metal and are very expensive, and lack stability.
Regarding EL elements using a copper atom, there is a study of Zhang et. al. (Zhang, J.; Kan, S.; Ma, Y.; Shen, J.; Chan, W,; Che, C. Synth. Met. 2001, 121, 1723-1724), but, no great improvement in emission efficiency is observed.
Further, examples of metal pyrazole complexes have been reported until now in Kim, S. J.; Kang, S. H.; Park, K.-M.; Kim, H.; Zin, W.-C.; Choi, M.-G.; Kim, K. Chem. Mater. 1998, 10, 1889-1893; Barbera, J.; Elduque, A.; Gimenez, R.; Lahoz, F. J.; Lopez, J. A.; Oro, L. A.; Serrano, J. L. Inorg. Chem. 1998, 37, 2960-2967; Enomoto, M.; Kishimura, A.; Aida, T. J. Am. Chem. Soc. 2001, 123, 5608-5609; and Dias, H. V. R.; Diyabalanage, H. V. K.; Rawashdeh-Oary, M. A.; Franzman, M. A.; Omary, M. A. J. Am. Chem. Soc. 2003, 125, 12072-12073. Regarding a metal pyrazole complex, although Enomoto et. al. found strong photoluminescence exhibited by irradiation of ultraviolet rays, there has been no report on EL emission.